Gas turbines are known to comprise one or more combustion chambers or combustors including several burners, wherein a fuel is injected, mixed to an airflow and combusted to generate high-pressure flue gases that are expanded in a turbine. During operation of the gas turbines, oscillations may be generated and thermoacoustic vibrations occur. This does not only lead to acoustic disturbances, but can also cause mechanical damages to the components of the gas turbine. In order to reduce the thermoacoustic vibrations during the operation of gas turbines, it is known to install in the combustion systems so-called damping devices, in particular Helmholtz dampers. Such Helmholtz dampers comprise an enclosure defining a damping volume, from which a neck portions extends and in which a flow path for cooling air is provided such that the temperatures during operation, in particular at the neck portion of the Helmholtz dampers, remain within predetermined limits. Therefore, such damping devices for combustors or burners of gas turbines require a sufficient supply of cooling air, which is guided to the neck portion of the damper.
On the other hand, such gas turbines have to be provided with sealing means between separate parts of the turbine, in particular at the interface between the burners and combustors or at other interfaces, e.g. between a combustion liner and a transition piece. For the purpose of sealing between the components of gas turbines, it is known to use circumferential metal seals. Such flexible annular seals are utilized in gas turbines for providing a sufficient sealing effect between concentrically assembled gas turbine combustor components. In order to guarantee a long lifetime and efficient sealing between the components of gas turbines, the sealings of the combustor components are conventionally equipped with means for cooling the sealing during the operation of the gas turbine. Also in order to avoid an oxidation of components, an airflow of cooling and purging air is required to be directed in particular to the tip part of such sealings of combustor components. The known sealings, e.g. hula sealings, are therefore not only complex in their design, but require also an additional supply of cooling and purging air within the gas turbine, which adds to the required airflow of cooling air necessary for the above-mentioned damping devices.
These different airflows for the purpose of the cooling of damping devices and seals can cause increased NOx emissions and may lead to problems with regard to the stability of operation of the burners and combustors. Besides the possible negative impacts on NOx and CO emissions, an insufficient cooling of the so-called Helmholtz dampers reduces also the damping efficiency during the operation of the gas turbines. In the known devices for damping and sealing, it is therefore necessary to provide respective cooling air supply means for both purposes, namely the thermoacoustic damping as well as the cooling of sealing means at the interfaces of combustor components. The design of the damping and sealing devices is therefore rather complex and leads to an increase in the overall costs of such gas turbines and has a negative impact on the operation efficiency and is disadvantageous with regard to environmental restrictions.
In view of these disadvantages, it is an object of the present invention to provide a Helmholtz damper for a combustor or burner of a gas turbine for a low-emission operation with high efficiency with regard to the thermoacoustic damping and sealing of components in the combustors. Furthermore, with the damper according to the present invention, the influence of the damping and sealing systems on the stability of operation should be reduced.
According to the present invention this problem is solved by means of a Helmholtz damper with the features of claim 1. Further developments and preferred embodiments of the invention are subject matter of the dependent claims.
The Helmholtz damper for a combustor or combustor components of a gas turbine according to the present invention comprises an enclosure defining a damping volume, from which a neck portion extends and which has a flow path for cooling and/or purging air with an inlet opening and an outlet opening to said enclosure, wherein said outlet opening is formed in the neck portion of the enclosure, and wherein the damper is characterized in that a seal is arranged at said neck portion adjacent to said outlet opening for cooling and purging air such that a cooling effect of said seal is provided. That means, the Helmholtz damper of the invention is not only specifically adapted for the purpose of thermoacoustic damping, but at the same time provides an efficient sealing means for adjacent components of the combustor interfaces. A seal is arranged at the area of the outlet opening of the cooling airflow path such that the seal is directly cooled by the cooling and purging air coming from the interior of the Helmholtz damper. By means of this, a separate supply of cooling air to the damper and the seal is avoided. This leads to a reduction of complexity in the design since no separate devices for the supply of cooling or purging air for the sealing on the one hand and for the thermoacoustic damping on the other hand are required anymore.
Furthermore, the total amount of airflow is considerably reduced, e.g. up to a half of the cooling airflow required in conventional devices for the operation of gas turbines. Also the operation of the combustors is more stable due to the reduction of mass-flow of air, and the NOx and CO emissions are hereby reduced. Nevertheless, the Helmholtz damper of the present invention has a high efficiency with regard to a limitation or elimination of vibration amplitudes during the operation of the combustor of the gas turbines, and at the same time the required sealing effect is provided. Due to the efficient cooling of both elements, namely the damper enclosure and the seal, the operation range of the gas turbine equipped with such a Helmholtz damper is large. Due to the constant air temperatures at particularly the neck portion of the enclosure of the damper as well as the seal arranged in the airflow of the cooling air, a stable operation and a long lifetime of the components are given.
According to an advantageous aspect of the invention, the Helmholtz damper is characterized by a common supply of cooling and purging air for the damper and the seal. The damper and the seal, which is provided at the neck portion of the Helmholtz damper, hereby share one single supply means for cooling air. The means for supplying cooling and purging air is, for example, attached to the inlet opening of the enclosure of the Helmholtz damper. The cooling airflow coming from the inlet opening passes through the inside of the enclosure and the neck portion of the damper, providing the required cooling effect of the damper for eliminating the thermoacoustic oscillations, and flows afterwards directly to the seal in the area of the outlet opening, the seal thus being cooled by one and the same cooling and purging airflow. By sharing a common supply of cooling and purging air in the Helmholtz damper, separate means for generating and providing cooling air are not necessary for the two components, i.e. the seal and the damping element. This results in an overall considerably reduced air consumption and therefore also in reduced costs and in a more stable operation of the gas turbine, since the added cooling air in the combustion chambers is reduced as compared to combustion systems with separate means for providing cooling air to the seal and the damping devices.
According to an advantageous aspect of the Helmholtz damper of the present invention, the seal is an integrated part of said neck portion of the enclosure of the damper. By means of this, the seal is a part of the Helmholtz damper itself, or it is firmly attached to the neck portion of the enclosure. This facilitates the installation of the damping and sealing system in a combustion system of a gas turbine. For example, it is not required to provide separate attachment means for the seal and the damping device, as was the case in the prior art. Furthermore, with the seal as an integrated part at the neck portion of the Helmholtz damper, the cooling of the seal is enhanced: the neck portion already cooled by the cooling airflow transmits the cooler temperature directly to the sealing part, which is an integrated part of the neck portion of the damper.
According to a further advantageous aspect of the Helmholtz damper according to the invention, the neck portion of the enclosure of the damper has an extended length for the accommodation of said seal and/or fastening means for fastening the damper within a combustion system of a gas turbine. The length of the neck portion is extended in view of conventional Helmholtz dampers of the prior art, in which a rather short neck portion is usually given. With the extended neck portion, the fastening of the Helmholtz damper to the interfaces of a combustion chamber is facilitated. Furthermore, with the extended length, the neck portion is specially adapted for the arrangement of a seal in this area where the cooling airflow exits from the enclosure of the Helmholtz damper. For example, the attachment means for mounting the damper to a transition wall or to an interface in the combustion chambers is provided at one side of the neck portion, whereas the seal is mounted or provided at the opposite side of the neck portion. The complete Helmholtz damper is hereby fixedly attached to the interface or wall of the combustor, so that the damping effect is guaranteed. The seal, which is on the other side of the neck portion, can undergo sufficiently large displacements in an elastic range without losing its sealing efficiency. By means of these measures, a combined efficient thermoacoustic damping and sealing is realized by means of one and the same Helmholtz damper device.
According to a further advantageous aspect of the Helmholtz damper of the invention, the outlet opening for the cooling and purging airflow is provided with flow guiding means directed to said seal at the neck portion of the enclosure. A concentrated stream of cooling airflow is hereby directed to the seal, which is arranged in the area of the outlet opening of the Helmholtz damper in said neck portion. An increased cooling effect of the seal is hereby achieved. The seal and the neck portion of the Helmholtz damper are thereby protected from hot combustion gases flowing in the adjacent combustion areas of a combustor or a burner of a gas turbine. By means of such flow guide elements, which can, for example, be given in the form of airflow guide blades, specific flow patterns can be created in the area of the seal and the neck portion of the Helmholtz damper, so that the cooling effect during the operation of the gas turbine can be adapted to respective designs of combustion chambers or gas turbines and the flow paths of hot gases.
According to a further advantageous aspect of the Helmholtz damper according to the invention, the neck portion of the enclosure is provided with fastening means to an interface of a combustion chamber. The interface can, for example, be a liner-front-panel interface or a liner-carrier interface in a premix combustor or in a so-called SEV combustor. Furthermore, the fastening means at the neck portion can be adapted for a mounting of the combined damper and sealing device according to the invention on a front panel of a burner between a liner or further components of a gas turbine. Examples of fastening means are rectilinear wall portions for screws or welding in the sense of mounting flanges. Other types of fastening means may also be provided.
According to a further advantageous aspect of the Helmholtz damper of the invention, the seal is arranged on a circumferential outer side with regard to said enclosure of the damper. That means, the damper is in a more radial inner position as compared to the seal, which is at a radial outer position with regard to the enclosure forming the damping body. According to an alternative embodiment of the invention, the seal is arranged on a circumferential inner side with regard to the enclosure of the Helmholtz damper. Depending on the respective local hot gas flow pattern in the combustion system of the gas turbines, it might be beneficial to place the seal radially inside or outside of the damper. By means of the modification of the position of the seal with regard to the enclosure of the Helmholtz damper, the sealing and damping efficiency of the device can be further increased. For example, the outlet opening and neck portion of the enclosure can be realized in a lateral position of the enclosure, and the seal on the neck portion is either provided on the radial inner side or on the radial outer side of this laterally offset neck portion. With such a form of damper/seal combination, the Helmholtz damper of the invention can be adapted to respective flow patterns of hot combustion gases and/or to the respective free spaces within the combustor system of a gas turbine. By means of these measures, the damper of the invention is specially adapted also for a mounting as a retrofit part, or it is well adapted for a later integration in burners or combustors as a retractable design.
According to a further advantageous aspect of the Helmholtz damper of the invention, the seal is segmented along a sealing surface. With a segmented seal, the transfer of heat from one part of the seal to the other parts is reduced. Furthermore, the segmented form allows a certain displacement of the segments of the seal in lateral directions due to a shrinking or deformation of components of the gas turbine. In an alternative form of realization, the seal is realized as a single piece, e.g. made of appropriate spring steel materials or the like.
According to a further advantageous aspect of the Helmholtz damper of the invention, the seal is a spring-type seal, and it is in particular a hula seal or an E-seal. With a spring-type seal, large displacements in an elastic range of the components of the turbine can be accommodated without loosing the required sealing efficiency of the seal part of the Helmholtz damper. An E-seal provides a seal, which is designed for low or moderate force conditions and high spring-back for achieving the large displacements required in some applications of combustion systems of gas turbines. A so-called hula seal is generally defined as a system of leaf springs formed into a round loop, which is used to seal a sliding interface joint or annular gap between two concentric elements, e.g. at an interface between a burner or combustor of a gas turbine. Both types of seal have been shown to be especially well adapted for an integration in combination with the Helmholtz damper as it is the subject matter of the present invention.
According to a further advantageous aspect of the Helmholtz damper of the invention, the enclosure of the damper is a single volume device. With the enclosure as a single volume device, the Helmholtz damper is specifically adapted for low-frequency pulsations and vibrations. Depending on the expected or actual form of frequencies and pressure oscillations in a combustion system of a gas turbine, the Helmholtz damper can be used accordingly.
According to an alternative form of realization of the invention, the Helmholtz damper is provided with an enclosure, which is a segmented volume device. A segmented volume device is well adapted for providing an efficient damping in case of high-frequency pulsations. In both cases, a segmented volume device and a single volume device, in particular the neck portion of the enclosure is cooled by a cooling airflow coming from an inlet opening and passing through the neck portion to an outlet opening. The temperature range of the enclosure of the Helmholtz damper remains in a predefined temperature range, so that no considerable modification of the damping function is created during the operation of the gas turbine. A more predictable and more efficient thermoacoustic damping is hereby achieved.
According to a further advantageous aspect of the invention, the enclosure of the Helmholtz damper is designed for varying the damper volume. The Helmholtz damper of the invention is provided with an adjustable volume for the purpose of damping different ranges of frequencies or vibrations. A more flexible use in a broader range of applications is hereby given. The volume of the enclosure may, for example, be modified by means of varying the segment size of the enclosure, the neck length of the neck portion of the enclosure, and/or the size of the outlet opening at the neck portion. For a skilled person in the art, there are further possibilities of adjusting the damping volume of such enclosures of Helmholtz dampers. With such changes and modifications of the damping volume, the efficiency with regard to the damping is furthermore increased, while at the same time the damper according to the invention provides an excellent sealing effect.
According to a further advantageous aspect of the invention, the Helmholtz damper is designed as a retrofit part for mounting in existing burners or combustors of gas turbines. A broader range of installation possibilities for the combined damping and sealing device of the Helmholtz damper of the present invention is hereby given. The Helmholtz damper can easily be integrated into existing designs and combustion systems of gas turbines. The damper can, for example, also be installed in such areas of interfaces between the combustors and burners of a combustion system, in which the conventional separate sealing devices and damping devices with respective separate cooling means have previously used. Such a form of a Helmholtz damper can also be realized as an independent device, which can regularly be inspected and, if necessary, replaced in a gas turbine. The maintenance is hereby made easier, and the operation safety margin is higher.